Fun with pointers

RedNifre

Hello!

I have several arrays and one pointer to the currently active array. Lets say I want to change the fourth LONG of the currently active array. How to do that?

  [noparse][[/noparse]...]
  arrayPointer := @array3

  ??arrayPointer??.LONG[noparse][[/noparse] 4 ] := 99


DAT
  array1 long blablabla
  array2 long blablabla
  array3 long blablabla
  array4 long blablabla

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Hydra in a LEGO NES:
http://forums.parallax.com/showthread.php?p=654788

potatohead

I like to use this

'Build Render Table
    repeat index from 0 to 189 * 4 step 4
      byte [noparse][[/noparse]@render_tab] [noparse][[/noparse]index] := 0           'set background color
      byte [noparse][[/noparse]@render_tab] [noparse][[/noparse]index + 1] := $20       'set sprite 0 x pos
      byte [noparse][[/noparse]@render_tab] [noparse][[/noparse]index + 2] := $40       'set sprite 1 x pos
      byte [noparse][[/noparse]@render_tab] [noparse][[/noparse]index + 3] := $00       'unused at present

That's an array of longs, but I need to modify bytes. @render_tab is an array of bytes, organized into longs. index is the address pointer. It's some code I'm working on right now.

In your case, since you are working with longs, you can just take the number of the long you want to modify, multiply it by 4, then do:

long [noparse][[/noparse]@your_array] [noparse][[/noparse]index] := value of long

, where index = number_of_long * 4

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CardboardGuru

Try LONG[noparse][[/noparse] arrayPointer][noparse][[/noparse] 4]:=99

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RedNifre

Ah, thanks alot!

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Hydra in a LEGO NES:
http://forums.parallax.com/showthread.php?p=654788

AndreL

There are a lot of ways to manipulate memory with SPIN both the reference manual and the HYDRA book have examples. The HYDRA book has pretty long section on this since there are a lot of features that you can do with pointers and casting that I wanted to cover, so make sure to check that out if you have the book.

Andre'